1. Field of the Invention
The present invention relates generally to apparatus that emit carbon monoxide, carbon monoxide monitoring and, particularly, to a system for monitoring the presence of carbon monoxide in the environment and for providing a plurality of signals at various concentration levels, including a signal for shutting off the apparatus.
2. Description of Related Art
Carbon monoxide is an asphyxiant gas that is colorless, odorless, tasteless, and non-irritating. This gas is formed from incomplete combustion and is a well-known health hazard to humans which may cause discomfort, sickness, and even death. Common sources of carbon monoxide include fires, gas appliances, heaters and furnaces, internal combustion engines used in power equipment and vehicles, and so forth.
Carbon monoxide is particularly dangerous when present in enclosed areas, such as building interiors, where inadequate ventilation can result in a build up of carbon monoxide concentration. Common sources of carbon monoxide in industry are equipment powered by engines that are intended for indoor use. Some examples of these sources include forklifts, small vehicles and hand-operated equipment that are powered by small engines such as floor strippers and polishers. When internal combustion engines are operated indoors, carbon monoxide can rapidly accumulate even if the area appears to be well ventilated. Because carbon monoxide is colorless, odorless, tasteless, and nonirritating, it can overcome the exposed person without warning.
Carbon monoxide affects people primarily by binding to hemoglobin in the blood, thereby preventing the normal transportation of oxygen to the tissues (tissue hypoxia). Oxygen is normally transported to the tissues in the body by reversibly binding with hemoglobin present in red blood cells as blood circulates through the lungs. As the blood moves through the body, the hemoglobin releases the oxygen for use in the body tissues. The blood then returns to the lungs, where oxygen again binds to the hemoglobin and the process repeats itself.
Tissues that are sensitive to hypoxia, such as the brain, heart, and exercising muscle are most affected by carbon monoxide. When hemoglobin binds with carbon monoxide it forms carboxyhemoglobin. Hemoglobin has an binding affinity for hemoglobin that is approximately 250 times greater than its affinity for oxygen. Because of its higher binding affinity, once carbon monoxide is bound to the hemoglobin, unlike oxygen, it is not easily released. Breathing fresh air for three to four hours after being exposed to carbon monoxide only eliminates half of the carboxyhemoglobin in the blood. Thus, exposure to carbon monoxide forms carboxyhemoglobin, which prevents the binding of oxygen and reduces the oxygen-carrying capacity of the blood. This in turn may produce weakness and confusion, and may deprive the person of the ability to seek safety.
While carbon monoxide present in the air causes the formation of carboxyhemoglobin in the blood, it is the build-up of carboxyhemoglobin in the blood which causes the adverse health effects. Real-time monitoring of ambient carbon monoxide may be implemented to indicate hazardous carbon monoxide concentrations. This is useful to warn an individual who may otherwise be exposed to high concentrations of carbon monoxide for short periods of time (e.g., when an individual briefly walks through an area or room where high concentrations of carbon monoxide are present).
Monitoring real-time carbon monoxide concentrations does not, however, indicate whether a hazard is present due to the build-up of carboxyhemoglobin in the blood of an individual exposed to low concentrations of carbon monoxide during a work shift. This scenario is present when an individual is in an environment for extended periods of time such as during the operation of equipment with an internal combustion engine.
The EPA has reported that a variety of physical effects occur in humans at different levels of carboxyhemoglobin. At 80% carboxyhemoglobinxe2x80x94death. At 60%xe2x80x94loss of consciousness; death if exposure continues. At 40%xe2x80x94confusion; collapse upon exercise. At 30%xe2x80x94headache, fatigue, and impaired judgement. Between 7-20%xe2x80x94statistically significant decreased maximal oxygen consumption during strenuous exercise in healthy young men. Between 5-17%xe2x80x94statistically significant diminution of visual perception, manual dexterity, ability to learn, or performance in complex sensorimotor tasks (such as driving). Between 5-5.5%xe2x80x94statistically significant decreased maximal oxygen consumption and exercise time during strenuous exercise in young healthy men. Below 5%xe2x80x94no statistically significant vigilance decrements after exposure to carbon monoxide. Between 2.9-4.5%xe2x80x94statistically significant decreased exercise capacity (i.e., shortened duration of exercise before onset of pain) in patients with angina pectoris and increased duration of angina attacks. Between 2.3-4.3%xe2x80x94statistically significant decreased (about 3-7%) work time to exhaustion in exercising healthy men.
Unfortunately, recognizing early warning signs of carbon monoxide poisoning is often difficult because early symptoms (e.g., headache, dizziness, and nausea) are nonspecific and may be mistaken for symptoms of other illnesses such as colds, flu, or food poisoning. Because it is colorless, odorless, and nonirritating, carbon monoxide can overcome exposed persons without warning. Additionally, prior use of equipment without incident may give users a false sense of safety, reducing their awareness of potential exposure hazards.
Therefore, it is desirable to outfit internal combustion equipment designed to be operated indoors with carbon monoxide monitors that will warn individuals operating the equipment when carbon monoxide concentrations pose a health threat. Warning signals may take the form of lights, digital displays, audible alarms, and engine kill switches that can shut an engine off if carbon monoxide concentrations exceed a specified level. Such apparatuses have been disclosed in the prior art in the form of a carbon monoxide monitor attached to equipment possessing an internal combustion engine. Carbon monoxide monitors have also been equipped with timers which will set off alarms or shut off engines if a critical threshold of ambient carbon monoxide concentrations has been exceeded for a period of time. U.S. Pat. No. 5,276,434, the entire disclosure of which is incorporated herein by reference, discloses such a monitor. Prior art monitors, while attempting to consider exposure to low carbon monoxide concentrations over extended time periods, fail to accurately estimate the true hazards to equipment operators resulting from the build-up of carboxyhemoglobin in their blood.
A need therefore exists for a carbon monoxide monitoring system that can warn when carbon monoxide exposure presents a threat to an operator of internal combustion engine equipment. Such monitoring system is needed to monitor ambient carbon monoxide concentrations and to estimate the operator""s carboxyhemoglobin level. Moreover, such monitoring system should provide comprehensive carbon monoxide monitoring, namely, indicating whether a hazardous situation exists from either short-term, high concentrations of carbon monoxide or extended exposures to low concentrations of carbon monoxide.
Accordingly, it is an object of the present invention to provide a comprehensive carbon monoxide monitoring system for use with an apparatus containing an internal combustion engine.
It is a more particular object of the present invention to provide a carbon monoxide generating apparatus such as a floor polisher powered by an internal combustion engine or a power washer with a heat chamber wherein fuel is burned and having a carbon monoxide monitoring system that warns of the presence of hazardous levels of carbon monoxide during the operation of the apparatus.
It is a further object of the present invention to provide a carbon monoxide monitoring system that measures carbon monoxide in the environment and estimates carboxyhemoglobin levels in the blood of an individual exposed to the environment.
Briefly, a system for monitoring carbon monoxide in an environment embodying aspects of the invention is for use with an apparatus containing an internal-combustion engine emitting carbon monoxide. The system includes a carbon monoxide sensor which samples the air and supplies an electrical signal representative of the concentration of carbon monoxide in the environment. The sensor supplies the electrical signal to a processor which calculates a corresponding concentration of carbon monoxide. If the concentration of carbon monoxide exceeds a threshold concentration, the processor provides an output signal to a device which then indicates the presence of carbon monoxide above the concentration threshold. The processor also calculates a time weighted average concentration corresponding to the concentrations of carbon monoxide that were measured over time. If the time-weighted average concentration exceeds a threshold, the processor provides an output signal to a device which then indicates the presence of carbon monoxide above the time-weighted average threshold.
In another aspect, the invention is directed to a carbon monoxide emitting apparatus equipped with a carbon monoxide monitor and an internal-combustion engine emitting carbon monoxide. The carbon monoxide monitor includes a carbon monoxide sensor that samples the air and supplies an electrical signal representative of the concentration of carbon monoxide in the environment. The sensor supplies the electrical signal to a processor which calculates a corresponding concentration of carbon monoxide. If the concentration of carbon monoxide exceeds a threshold concentration, the processor provides an output signal to a device which then indicates the presence of carbon monoxide above the concentration threshold. The processor also calculates a time weighted average concentration corresponding to the concentrations of carbon monoxide that were calculated over time. If the time-weighted average concentration exceeds a threshold, the processor provides an output signal to a device which then indicates the presence of carbon monoxide above the time-weighted average threshold.
In further aspect, the invention is directed to a carbon monoxide monitor. The carbon monoxide monitor includes a carbon monoxide sensor that samples the air and supplies an electrical signal representative of the concentration of carbon monoxide in the environment. The sensor supplies the electrical signal to a processor which calculates a corresponding concentration of carbon monoxide. If the concentration of carbon monoxide exceeds a threshold concentration, the processor provides an output signal to a device which then indicates the presence of carbon monoxide above the concentration threshold. The processor also calculates a time weighted average concentration corresponding to the concentrations of carbon monoxide that were calculated over time. If the time-weighted average concentration exceeds a threshold, the processor provides an output signal to a device which then indicates the presence of carbon monoxide above the time-weighted average threshold.
Other features of the present invention will be in part apparent to those skilled in the art and in part pointed out in the detailed description provided below.